The present invention concerns a process and a device designed for monitoring the cut-to-print quality in a line of machines converting sheet-shaped workpieces into a package.
Package production, for instance of cardboard, whether or not corrugated, extends through at least three successive phases, i.e. printing and cutting, as well as folding and gluing. The quality of the final product thus depends on the quality of the different phases, each considered individually.
The present invention concerns essentially the monitoring of the cut-to-print quality. Up to now, printing was checked visually after the offset or rotogravure printing machine, i.e. an assistant trained for knowing the print quality criteria can, with sufficient practical work, gather an adequate amount of knowledge, experience and skill allowing him, with a short glance on the multi-color print provided in the corresponding printing units of a printing machine, to judge the print quality, i.e. to decide whether the print under examination is acceptable. If the print is actually acceptable, the printing machine continues its production which will then be carried towards the subsequent, i.e. cutting, machine. If the print is not acceptable, the operator of the printing machine will be informed thereof and will proceed with the control of the printing machine to the necessary modifications for the correction of the shortcomings of the print. Attention is drawn to the fact that printing can be done with the workpiece still having the shape of a web, or else of successive sheets travelling through.
The following shortcomings, though, can be attributed to the above considerations, i.e.:
checking cannot be permanent;
only an experienced and skilled person is able to check;
checking is not reliable since erroneous judgments are very likely to occur on account of objective criteria regarding the printing or cutting quality, this contingency being likely to grow with the scrutinizer's increasing fatigue;
the scrutinizer does not have the means for checking quality statistically in the course of production by recording the number of sheets meeting with certain printing quality criteria, for instance by proceeding to comprehensive simple and simultaneous checking of the four main quality criteria of which a description will follow hereafter with regard to printing and cutting as might be done in a package producing machine line;
such checking is monotonous and tiresome.